Help please

[ado]

I am new to PixInsight and have come up against an unusual problem that has brought me to a stop very early on in the processing procedure.
I have three reasonably good narrowband images. I get as far as Dynamic Crop and then follow the procedure exactly as shown in videos and help files. Ending up with three cropped images. The problem is they are all different sizes, for example; 2672 x 2152, -  2651 x 2144, -  2658 x 2143,  Close, but of course they cannot be Channel Combined. I think I have tried every combination with the Dynamic Crop, even re-adjusting the size of each image manually before the crop. This gives me three images I can stack but the scale is wrong so they do not align on top of each other (I can move them with Channel Match).
I have also tried this.
If I do not Dynamic Crop at all, but Star Align, I stack and then a simple Crop, but I cannot find out how to separate and colour the channels (it’s a bit different to Photoshop). I just end up with mono frames even after Convert to RGB Colour. I know I am just missing a procedure here but I don’t know which one.
I am very keen to give this program a go but I cannot get past this point.
Thanks in advance.  Adrian                         

[Juan Conejero]

Hi Adrian. Welcome to PixInsight Forum.

You shouldn't crop the images before StarAlignment. Just align the three images, then use ChannelCombination to generate an RGB image if you wish. Or, since you are working with narrowband data, much better if you use PixelMath to generate an RGB combined image with an arbitrary palette. There are plenty of examples and tutorials out there for these tasks.

In a nutshell:

- Let's say that you have three images: Ha, O3 and S2 (on PixInsight Resources: Set image identifier)

- Open PixelMath and type the following in the R/K, G, anf B edit fields, respectively:

S2
Ha
O3

- In the Destination section of PixelMath, check the Create new image option and select color space=RGB. Leave the rest by default.

- Apply PixelMath (blue triangle, drag, drop) to one of the images.

- A new RGB image will be generated with your combination.

- If you want to fine tune the palette (you'll want for sure), you can try with expressions as for example:

0.5*S2 + 0.5*Ha
0.15*Ha + 0.85*O3
O3

This is just an example, you should try with different factors.

[sreilly]

And though what Juan suggested is the best approach, you can also use dynamic alignment and then combine but you'll still need to crop the final combined image. You'll need to do two images at a time such as Ha and SII, save the registered results, and then Ha and OIII and register saving the results. Open the 3 registered images, combine, and then crop.

Steve

[ado]

Hi.    Thanks Juan and Steve, much appreciate your help.
Just out of interest have you come across the initial problem I was having with DynamicCrop. All the photos were taken with the same camera etc. with no rotation other than Meridian flip. How can they be of different scales? Is this possible with different filters. I did have a similar problem in Photoshop and found changing the % size rather than the pixel size improved it although it was not perfect.
Thanks again.    Adrian

[sreilly]

Interesting you should mention that as I hadn't noticed that before. I recently calibrated some images using MaxIm because I like the way you can remove the hot and dead pixels. After saving the images, all taken using MaxIm I noticed a difference in actual physical file size. I can only think that how they were taken can attribute to that difference. The file size is 5,243 kb vs. 5,237 kb although they are both 2004x1336 pixels (binned 2x2 STL-11002M images). The difference must be in the actual FITS header info. The larger (6 kb) files were taken using ACP and MaxIm while the smaller size were taken using MaxIm without ACP in control. But both are the same pixel size. The only time I've seen a difference in pixel size is with different bin rates. I take my luminance images binned 1x1 and color at binned 2x2 and when both masters are processed I use Dynamic Align to register them.

With your images, are these different sized images taken using the same software and the processed in PI? What camera, software are you using?

-Steve

[ado]

Hi Steve.
I think my problem is different to yours. In my case my Master frames are different physical sizes in pixels. In width say about 10 to 20 pixels (and a bit in height). So I have a wider photo covering the same area of sky, trimming the width and height does not solve the problem because the scale is different. For example looking at the stars while trying to align, a blue master (star) would show an offset to the left on the left side of the frame and be offset to the right on the right side of the frame. I hope that description makes sense. And I know what you are saying, ‘’that’s impossible from the same camera’’. This is not a PixInsight problem as it was the same in Photoshop. My capture software is Sequence Generator Pro. But I think the problem must be in the optical train, and the only thing that changes are the filters!    Any thoughts would be appreciated.
I used your recommendation of Dynamic Alignment, it worked well but I then split the channels and re-combined in PixelMath with ColourSpace=RGB and ended up with a mono image? A bit more work needed. I tried Juan’s method but of course the images will not align and Channel Combination will not work with different sized images.
Regards.   Adrian

[sreilly]

What camera are you using and what is the native format? Are all the raw files the same or are the dimensions changing after some process id applied? It sounds like an issue with the master frames so I'm guessing all the individual frames are identical in size? What software and method are you using to create the masters? I know that aligning the images might have some options that would possibly create a larger master frame by adding the offset to sides (overlap) but I don't remember the term used for the alignment method.

If all the raw files aren't the exact same size and there is no difference in bin rates between the images then you may have a camera or driver issue. Is all your processing being done to the raw images in PI or are you doing some in one program and then bringing into PI?

-Steve

[ado]

Hi Steve.
I am afraid I have led you away from the main direction of this Forum.
The camera is an SXVR-H694.  2750 x 2200 pixels 12.48 x 9.98mm. chip. 4.54 x4.54 pixel size. The individual frames are identical in size. But the masters (all Raw and bin 1x1) are 2 or 3,0000 difference in size, not much out of 6,050,000. Before PixInsight I used Nebulosity for combining and stacking. I am hoping to do all the processing in PixInsight in the future and as I said earlier the Dynamic Alignment you recommended worked, I just have the problem converting to colour afterwards.
Regarding your last paragraph I will have to do a bit more research there, I never thought of a camera problem.
Thanks.    Adrian